A variety of neurological and psychiatric disorders are associated with alterations in synaptic plasticity, including Alzheimer's disease, schizophrenia, and Down syndrome. Each of these conditions has also been suggested to involve pharmacological modulation by multiple neurotransmitter receptors, including both the N-methyl D-aspartate receptor (NMDA) and cholinergic nicotinic receptors, particularly the a7 receptor. Understanding the role of such receptors in synaptic alterations and development may thus be crucial for the development of novel therapeutic approaches. The cellular basis for neural plasticity that underlies learning and memory involves a combination of functional and structural alterations in neurons and synapses. While much attention has focused on N- methyl-D-aspartate receptor (NMDAR)-dependent postsynaptic mechanisms involved in long-term change, presynaptic mechanisms are also crucial to such these processes. As seen in postsynaptic mechanisms of synaptic modification, presynaptic glutamatergic receptors including presynaptic NMDA receptors have been proposed to be involved in the regulation of axonal branching and bouton formation. Our preliminary data demonstrate that the axonal a7 nicotinic acetylcholine receptors (nAChR) modulate the location and size of glutamatergic presynaptic boutons and presynaptic NMDAR-mediated glutamatergic transmission in cortical cultures, suggesting that the axonal a7 nAChR and presynaptic NMDARs may be intrinsic factors and signaling mechanisms that mediate synaptogenesis and structural plasticity of glutamatergic axons. In the present proposal, we will extend this work through detailed assessment of these events in models of development and in neonatal brain. This will also allow us to ascertain the role of nAChR-NMDAR interactions in synaptogenesis and structural plasticity, and the temporal periods for such events. We will begin with complete definition of the pharmacological mechanism underlying the presynaptic interactions of a7 and NMDAR. We will then assess the development course of these events to define the critical period during which such interactions occur using neuronal cultures, hippocampal slice cultures and neonatal animals. Collectively these experiments will allow us to identify the mechanisms that mediate the presynaptic interactions of nicotinic and glutamatergic systems, and provide a basis for interpreting these results in the contexts of specific disorders. This will allow new investigations directly targeting these diseases.